A series of laboratory experiments will be performed over the next 3 years to determine the functional activation of T-lymphocytes and dendritic cells derived from psoriatic lesional skin. Our studies with treatment of psoriasis indicate reversal of keratinocyte activation in psoriatic lesions when cytotoxic or cytostatic agents for T-lymphocytes are given in vivo to patients with this disease. These observations strongly suggest that immune cells or their products are mediating or inducing epidermal changes in this disease. However, direct proof of this idea is lacking. The proposed experiments are a direct test of the pathogenicity of T-lymphocytes and/or dendritic cells isolated from psoriatic lesions. Characterization of their activity is critical to the assumption that these cells are disease-mediating.